The present invention concerns generating control signals for use in pulse width modulation.
Pulse width modulated signals are useful in many applications. A pulse width modulated signal may be generated, for example, by comparing a sawtooth signal and a feedback signal. The duty cycle of the resultant pulse modulated signal may vary, for example, based on the percentage of time the voltage of the sawtooth signal is greater than the voltage of the feedback signal.
In some prior art systems, a pulse width modulation (PWM) control circuit system requires three control signals. In such a system, control signals include, for example, a sawtooth signal, a synchronization pulse, and a square wave. As more completely illustrated in the Description of the Prior art below, it is often the case that control signals are slightly out of synchronization because of propagation delays inherent in the circuitry which generates the control signals. Because the control signals are out of synchronization, delay must be added within the PWM control circuit system to compensate. However, it is difficult to precisely determine and supply the correct amount of delay. Therefore, a PWM control circuit system may become non-linear or unstable at the extremes of its operating range. It is desirable, therefore, to develop a control signal generator which generates control signals in such a way that an incorporating PWM control circuit system will maintain linearity even at the outer limits of its operating range.